Lumbar spine or back pain is one of the most important problems in orthopedics and neurosurgery today. Two key ways of treating this malady, lumbar fusion and stabilization, are critically discussed in the forty-three papers in this volume. They represent the best of the contributions to the 5th ICLFS, carefully selected and edited to give a good overview of recent knowledge and the state of the art.Lumbar spine or back pain is one of the most important problems in orthopedics and neurosurgery today. Two key ways of treating this malady, lumbar fusion and stabilization, are critically discussed in the forty-three papers in this volume. They represent the best of the contributions to the 5th ICLFS, carefully selected and edited to give a good overview of recent knowledge and the state of the art.1 Principles of Lumbar Fusion and Stabilization.- 1.1 Biomechanics of Lumbar Spine Instability.- 1.2 The Myth of Solid Posterior Lateral Fusion.- 1.3 Radiological Evidence of Posterior Lumbar Interbody Fusion.- 2 To Fuse or Not To Fuse.- Section I Determination of Segmental Instability.- 2.1 The Role of External Fixation as a Predictor of Fusion Success.- 2.2 Assessment of Segmental Spinal Instability Using Magnetic Resonance Imaging.- 2.3 Intraoperative Measurement of Lumbar Spinal Stiffness.- Section II The Merits and Demerits of Lumbar Fusion.- 2.4 The Long-Term Effect of Lumbar Spine Fusion: Deterioration of Adjacent Motion Segments.- 2.5 A Critical Analysis of Motion of the Lumbar Spine Adjacent to an Interbody Fusion: A Clinical Radiological Study and Biomechanical Cadaveric Study.- 2.6 Anterior Interbody Fusion for Degenerative Spondylolisthesis: The Long-Term Clinical Results.- 2.7 Clinical Results of Lumbar Fusion for Heavy Workers with Lumbar Disk Herniation.- Section III Multi-Segmental Spondylosis.- 2.8 Multi-Segmental Spondylosis: An Overview of Presentations at the Fifth International Conference on Lumbar Fusion and Stabilization.- 2.9 Patient Selection for Stablcu